The present invention relates to a measuring device comprising two or more sensors for one or several values to be measured, these sensors being arranged so as to be connected to an electric power supply and to provide, through output lines, signals which are a function of the value to be measured, the device further comprising transmission and processing devices for the output signals from the sensors.
The invention is more particularly applicable to a device for indicating the absolute angular position of a shaft, comprising position sensors with a rotatable member, the rotatable member of a first sensor being coupled mechanically with said shaft, and the rotatable members of the other sensor or sensors being coupled successively with that of the first sensor through gears, these sensors being arranged so as to be supplied with a sinusoidal or a pulsed voltage and to provide output signals which are a function of the angular position of their rotatable member.
In such devices, the sensors must be connected, on the one hand, to a power supply and, on the other hand, to a device for processing their output signals. In the case of inductive sensors, for example of the resolver type, these output signals appear at the terminals of two phases and, accordingly, require up to four lines per sensor for their transmission to the processing device, generally located at a certain distance from the sensors. When used for measuring the angular position of a shaft, the number of sensors which are needed depends upon the operational range of the device, i.e. on the maximum number of revolutions of the input shaft that the device can indicate, so that a large number of connecting lines are often necessary, which in practice constitutes an important drawback.
In order to limit the number of connection lines which are necessary in this particular case, one can use, between the different sensors, gears with a high reduction ratio, so as to reduce the number of sensors necessary for a given operational range. However, this solution requires sensors and gears which are highly accurate and, accordingly, it leads to relatively high cost prices for the whole device.
The invention is aimed at providing a device of the aforementioned type in which the number of connection lines between the sensors, a signal processing device and a power supply device, can be reduced to a significant extent, while at the same time achieving a cost price reduction for the whole device, which can be substantial in certain cases.